Hermann Detzner
Hermann Detzner was the last German soldier to surrender in WWI. He and his unit (~200 natives and 4 officers) roamed parts of Papua New Guinea until Feb. 1919,3 months after the end of WWI.
They managed to escape Australian patrols by hiding in the jungle and the mountains. However they did not really try hard to hide: they always flew their flag and sang German marching songs when moving from one place to the other.
http://en.wikipedia.org/wiki/Hermann_Detzner